The present invention relates to inkjet printing devices, and more particularly to the use of patterned thin film microheaters for assembly of inkjet printhead assemblies.
Thermal inkjet (TIJ) technology is widely used in computer printers. Very generally, a TIJ includes a printhead typically comprising several tiny controllable inkjets, which are selectively activated to release a jet or spray of ink from an ink reservoir onto the print media (such as paper) in order to create an image or portion of an image. TIJ printers are described, for example, in the Hewlett-Packard Journal, Volume 36, Number 5, May, 1985, and Volume 39, Number 4, August, 1988.
Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on the print medium. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the print medium as the printhead is moved relative to the print medium.
In one known design, the inkjet printhead generally includes ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice, a metal orifice plate or nozzle member in which the orifices are formed in the required pattern, and a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and consequently, causing a droplet of ink to be ejected through an associated orifice onto the print medium.
An exemplary inkjet cartridge is described in U.S. Pat. No. 4,500,895, entitled xe2x80x9cDisposable Inkjet Headxe2x80x9d, and is assigned to the present assignee.
Another inkjet printhead is described in U.S. Pat. No. 4,683,481, entitled xe2x80x9cThermal Ink Jet Common-Slotted Ink Feed Printheadxe2x80x9d, wherein ink is fed from an ink reservoir to the various vaporization chambers through an elongated hole formed in the substrate. The ink then flows to a manifold area, formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. This design is known as a center feed design, whereby ink is fed to the vaporization chambers from a central location and then distributed outwardly into the vaporization chambers.
In TIJ pens it is necessary to connect the ink reservoir to the printhead. The size of this connection affects the design of the printer that the pens are used in. An ideal reservoir-to-printhead coupler, from a print design point of view, would be no longer than the TIJ head is long, and would be high or tall enough to allow the drive and pinch wheels to get as close to the printhead as possible. Any increase in the size of this coupler will compromise the paper handling ability, which may affect the print quality, and increase the size of the printer.
In one exemplary spring bag pen design, the pen frame of a first molded material is lined with a second molded material, such as polyethylene, on the inside to produce a surface suitable for staking the films of the spring bag. The first molded material from which the frame is made could be, for example, an engineering plastic, and provides the necessary structure for the pen which could not be accomplished with the second molded material. In this design, the fluid connection of the first and second molded materials needs to designed in such a way as to provide a space-efficient, leak-resistant connection.
Conventional methods of connecting plastic materials, including those used in TIJ pens, include the use of glue, seals, such as gaskets or 0-rings, or mechanical press fits. In these cases two or more separate parts are fabricated and assembled together to form a single unit. Each part must be designed and sized with respect to its needs in manufacturing, structural integrity, and with the tolerance of the mating part in mind. Such joints as these take up space, and their reliability can be affected by the part tolerances, surface finishes, and the assembly operation and the material properties of the adhesive.
Commonly assigned application Ser. No. 07/853,372 describes a leak-resistant joint between the first and second molded materials, wherein the first and second molded materials have different shrink rates. As the first material cools from a molten state, the second molded material is molded about a standpipe formed of the first molded material thereby creating a tight joint between the two molded materials. In each of these exemplary devices, the TIJ printheads are assembled using polymer substrates and thermoset adhesives which are cured by heating the entire printhead/pen assembly. This procedure results in large deformations due to coefficient of thermal expansion mismatches and substrate processing defects. In addition, this heating of the entire assembly frequently effects performance of other parts or limits the kinds of assembly sequences and automation strategies that can be pursued. Furthermore, some materials which might be beneficial can not be used in the assemblies since the entire assembly is subjected to this curing process.
The invention makes use of patterned thin film resistors (microheaters) for assembly of the inkjet printhead assemblies wherein once activated, the microheaters cure the interfaces between different parts of the assembly thereby alleviating the need for curing the entire printhead assembly.
According to one embodiment of the invention, an apparatus for assembling an inkjet printhead is disclosed. Other embodiments discussed hereinafter include, but are not limited to: reflowing thermoplastic or thermoset materials such as thermoset polymers, all of which are referred to hereinafter as temperature curable adhesive. Still other embodiments contemplate reflowing a solder or brazing material. The heating apparatus comprises a microheater and a temperature curable adhesive disposed proximate to the heater resistor.
The microheater comprises a heater resistor with electrical contacts referred to as an input port and an output port. A first electrical conductor, coupled to the input port of the heater resistor, receives a first voltage and a second electrical conductor, coupled to the output port of the heater resistor, receives a second voltage. A curing effect in the adhesive is produced by heat generated by current flow caused by the application of a first voltage to the first electrical conductor and a second voltage to the second electrical conductor. A voltage differential across the input and output ports causes a current to flow through the heater resistor, elevating its temperature.
According to another embodiment of the invention, an inkjet printer cartridge is disclosed. The inkjet cartridge comprises a printhead comprising a top side and a bottom side, the bottom side having a microheater, and a printhead attachment. The microheater comprises a heater resistor comprising an input port and an output port. A first electrical conductor, coupled to the input port of the heater resistor, receives a first voltage and a second electrical conductor, coupled to the output port of the heater resistor, receives a second voltage. The printhead attachment is disposed below the bottom side of the printhead, wherein the printhead attachment is affixed to the printhead by an application of a first voltage to the first electrical conductor and a second voltage to the second electrical conductor.
According to another embodiment of the invention, a method for assembling an inkjet printhead assembly is disclosed. A heater resistor is patterned onto a bottom surface of a printhead. A printhead attachment is aligned in a desired position wherein a surface of the printhead attachment is in contact with the heater resistor. A voltage drop is applied across a heater resistor which produces an electrical current in the heater resistor. A temperature increase in the heater resistor and an area proximate to the heater resistor is generated in response to the production of an electrical current thereby causing the printhead and printhead attachment to attach to the heater resistor.
According to another embodiment of the invention, a method for attaching pieces of a manifold using localized heating is disclosed. A thin film resistor is patterned onto a surface of a first half of a manifold with a first fluid passage. A second half of the manifold is aligned with a second fluid passage so as to provide a third fluid passage through the manifold, wherein a surface of the second half of the manifold is in contact with the thin film resistor. A voltage drop is applied across the thin film resistor to produce an electrical current in the thin film resistor. A temperature increase in the thin film resistor and an area proximate to the thin film resistor is generated in response to the production of the electrical current. At least portions of the first half and the second half of the manifold proximate to the thin film resistor are cured by the temperature increase thereby attaching and sealing the first half and the second half of the manifold to the thin film resistor.